1. Field of the Invention
The present invention relates to an image producing device utilized in computer graphics.
2. Description of the Related Art
In the computer graphics, an object to be displayed is made into a model by an assembly of a plurality of polygons. The respective vertexes of the polygons are represented by the columns of coordinates (x, y, z, w). The respective vertexes are coordinates-converted in accordance with a visual point position and then subjected to through-vision conversion in accordance with distances. In other words, the conversions are conducted in such a manner that a position far from a certain visual point is viewed to be small. The above sequential processing is called “geometry processing”. The vertex coordinates columns of each the polygon are obtained through the geometry processing. The vertex coordinates columns are transmitted to a graphic processing means as a display list (a graphic element list).
The graphic processing means draws a basic graphic in a frame memory in accordance with the display list. The drawing result is converted into an analog signal from a digital signal and then displayed on a display unit. Because the drawing result is updated every video rate, for example, every 1/60 seconds, a moving picture is displayed on a screen of the display unit. The above sequential graphic processing is called “rendering processing”.
In recent years, the semiconductor technology is remarkably progressive, and it is possible to realize that the frame memory and the graphic processing means are mounted on one LSI together. The graphic processing means includes a large number of circuits which are disposed in parallel with each other, and the parallel arrangement of the large number of circuits is compatible with the rendering processing where simple processing is frequently repeated. Also, if a memory is mounted in an unoccupied area, the band width of the frame memory can be widened. For that reason, the performance of the graphic processing means, in particular, a pixel driving speed can be significantly improved as compared with the conventional art. On the other hand, the performance of the corresponding geometry processing becomes relatively short. In other words, even if more polygons can be drawn in the frame memory, a process of calculating the vertex coordinates of the respective polygons is delayed.
In order to solve the above problem, it is effective to dispose geometry engines that execute the geometry processing in parallel with the graphic processing means. However, in drawing the graphic, because there are a large number of graphic contexts which are parameters to be predetermined, for example, a large number of clip regions, a large number of semi-transparent processing rates and so on, and parameters used in the individual geometry engines are different from each other, it is necessary to change over an input of the graphic processing means for each of the geometry engines. However, if the graphic contexts are changed over every times, an overhead at an input stage of the drawing means is too large. In addition, the change-over of the graphic context disturbs the coherence (consistency) of a cash memory and remarkably deteriorates the hit rate of the cash.